1. Field of the Invention
The present invention relates to an optical tomographic imaging apparatus for obtaining a tomgraphic image of a measuring object. In particular, the present invention relates to an optical tomographic imaging apparatus suited for obtaining a tomographic image of a measuring object such as a living tissue in a body cavity or the like.
2. Description of the Related Art
Electronic endoscope apparatuses are spread widely and used in various fields as the endoscope apparatus for observing inside of the cavity of a living body. The electronic apparatus obtains an image of a living body using reflected light reflected from the living body illuminated by illumination light and displays it on the monitor. Most of the endoscope apparatuses have a mouth forceps to allow a probe to be introduced inside of the body cavity through the forceps channel to perform a biopsy or treatment of the tissue within the cavity.
As the endoscope apparatus described above, an ultrasonic tomographic imaging apparatus that uses an ultrasonic wave and the like are also known. Further, an optical tomographic imaging apparatus using OCT (Optical Coherence Tomography) is proposed as described, for example, in U.S. Patent Application Publication No. 2004/0239942. In the apparatus disclosed in U.S. Patent Application Publication No. 2004/0239942, low coherence light outputted from the light source unit is split into measuring light and reference light, and the measuring light is irradiated on a measuring object, and the reflected light reflected from the measuring object is guided to the light combining means. Then, the reflected light is combined with the reference light by the light combining means, and the interference light produced by the mixing of the reflected light with reference light is measured through heterodyne detection or the like.
Here, when the measuring light is irradiated on the measuring object, a probe is used, which is inserted into the body cavity from the mouth forceps through the forceps channel. The probe includes an optical fiber for guiding the measuring light, and a rotatable mirror provided at the tip of the optical fiber for reflecting the measuring light in the orthogonal direction. The measuring light is irradiated on the measuring object in the body cavity from the probe, and the reflected light reflected from the measuring object is guided to the light combining means again through the optical fiber of the probe.
In the mean time, in the OCT measuring described above, resolution in the dept direction is dependent on the spectral width of the light used, that is, the greater the spectral width, the greater the resolution. Consequently, U.S. Patent Application Publication No. 2004/0239942 proposes to perform OCT measuring using an ultra-broadband light source.
Here, one of the optical guiding methods is known in which the measuring light, reflected light, and reference light are guided through optical fibers, in addition to the method in which they are guided through the atmosphere (bulk type). When the broadband light is guided through the optical fiber, however, the dispersion of the light becomes significant due to the dispersion properties of the optical fiber. This causes a problem that the resolution in the depth direction is degraded. Further, even if the OCT measuring is structured in the bulk type, there is no other way than to use an optical fiber for guiding the measuring light when obtaining a tomographic image inside of the body cavity. That is, when obtaining a tomographic image by inserting the probe into the body cavity, the image is degraded due to the dispersion properties of the optical fiber of the probe.
It is an object of the present invention, therefore, to provide an optical tomographic imaging apparatus that uses an optical fiber for OCT measuring, yet capable of preventing degradation of the resolution due to the dispersion properties of the optical fiber.